New economical design of SVC and passive filters to improve power quality at railway substation: a case study

Abstract

In electrified railways, harmonics and low power factor (PF) are typical power quality problems. The traction system of 25 kV, single phase, 50 Hz that exists in India has been taken for this case study. Most of the locomotives are single-phase and draw very high currents. The load is of highly variable nature and introduces high pollution into the power supply lines and distorts PF. The field measurement data in a tractions substation were collected and analyzed. The main objective is to identify an appropriate compensation strategy, which is cost-effective and reliable. This paper proposes a combined system of harmonic filters and thyristor-controlled reactors (TCRs) for PF improvement and reactive power compensation with new economical design of static VAR compensator (SVC). Generally, the SVC requires high-voltage switching of capacitors and inductors at very high cost. In the new concept, the voltage is stepped down to 600 V for reactors and divides into 32 parallel TCRs to handle high current in steps by switching without continuous control of firing angle. This technique makes system reliable and cost-effective. The TCR compensates reactive power dynamically and suppress the possibility of resonance between the SVC and the grid. The proposed system is verified using MATLAB simulation for harmonic filters. The simulated results are found to be quite satisfactory. The proposed solution is cost-effective and highly reliable than conventional SVCs and reduces harmonics to levels recommended in IEEE-519 standards.

Appendix

The ratings of firing scheme circuit for TCR components are R₁ = R₇ = 47 kΩ, R₂ = 220 Ω, R₃ = R₆ = 10 kΩ, R₄ = 2.2 MΩ, R₅ = 10Ω, C₁ = 680 pF, C₂ = 1000 μF, 25 V and Q = TL 188 Darlington pair.